This invention relates generally to the packaging and mounting of semiconductor devices in electronic circuits, and more particularly the invention relates to the packaging and mounting of high power semiconductor devices such as transistors which require heat sinks during operation.
RF power transistors are typically mounted on a ceramic platform which also supports a lead frame extending from the platform. The lead frame is interconnected with the transistor elements (e.g., emitter, base, and collector for bipolar transistor, and source, gate, and drain for field effect transistor), by wire-bonding or by solder bumps which directly engage both the lead frame and the transistor element contacts. The resulting structure, or pill, is then sealed by a lid to form the packaged transistor. The packaged transistor must be firmly mounted to a heat sink with heat from the semiconductor transistor being conducted through the ceramic platform to the heat sink.
Heretofore, a separate clamp has been employed for clamping the packaged pill-type transistor to the heat sink. However, this can result in uneven clamping force, cracking of the lid or body, and poor thermals, and ultimately lead to transistor failure. Other prior art mounting includes soldering the ceramic platform directly to the heat sink, which introduces new failure mechanisms such as thermal expansion mismatches and may increase thermal path resistance.
Disclosed in copending application Ser. No. 08/779,816 filed Jan. 6, 1997 (assigned to the present assignee) is an integral lid and clamp for a high powered transistor in which the lid is clamped directly to a heat sink without the need for a separate clamp.
The present invention is directed to an alternate power transistor device structure which does not require a separate clamp or a separate metal hold-down flange.